The invention concerns a tiltable metallurgical unit for smelting metal charge material, in particular ferrous material, and for post-treatment of the molten metal.
EP-0 240 485-Bl discloses an installation for the production of steel from scrap and possibly additive materials, comprising a blast furnace portion which has a bottom for receiving a liquid sump of pre-molten material and heating devices which open laterally into the lower portion of its interior, and with a hearth furnace portion which is integrally interconnected with the blast furnace portion and into which the pre-molten material can be transferred from the blast furnace portion. The hearth furnace portion directly adjoins the lower part of the blast furnace portion. Disposed between the lower blast furnace portion and the hearth furnace portion is an overflow weir by way of which pre-molten material which has collected in the trough or basin of the blast furnace portion continuously flows away into the hearth furnace portion, the bottom of which is arranged lower than the bottom of the blast furnace portion. The entire unit consisting of the blast furnace portion and the hearth furnace portion is tiltable, more specifically perpendicularly to a horizontal axis connecting the centre of the blast furnace portion to the centre of the hearth furnace portion. The hearth furnace portion has an eccentrically arranged bottom tapping for the steel and, in the side wall, a working door for drawing off the slag. Both the lower part of the blast furnace portion and also that of the hearth furnace portion have an interior which is circular in plan view, wherein the interior of the blast furnace portion is approximately tangential to the interior of the hearth furnace portion in plan and the transition from one interior into the other is of a reduced configuration. The heating means for the hearth furnace portion is an arc unit while the heating means for the blast furnace portion is a plurality of plasma burners which are arranged in the lower region of the shaft furnace portion distributed along the periphery thereof.
The bottom depression of the blast furnace portion is of a relatively shallow configuration and the upper edge of the overflow weir is of low height in relation to the bottom depression so that, at the beginning of a melting operation, only a small amount of the pre-molten material is retained in the bottom depression of the blast furnace portion and, after sump formation, the pre-molten material flows away continuously into the hearth furnace portion over the overflow weir. In order to prevent the molten material from congealing in the region of the overflow weir, on the one hand the inclination of the plasma burners is so set that the pre-molten material is overheated in a direction towards the overflow weir and on the other hand there is also a plasma burner between the blast furnace portion and the hearth furnace portion so that the pre-molten material can be overheated in the region of the overflow weir and a continuous discharge flow of the pre-molten material is guaranteed.
The metallurgical treatment in the hearth furnace portion begins as soon as half the bath depth is reached here. The molten material is heated to the tapping temperature by the additional supply of electrical energy. During that procedure pre-molten material continuously flows thereto from the blast furnace portion. When the tapping weight is reached in the hearth furnace portion, the material is tapped off in a slag-free condition by tilting of the unit, by way of an eccentric bottom tapping opening.
In the known installation, additional heat energy has to be supplied in the region of the overflow weir in order to prevent the premolten material from congealing in that region. In addition, during the treatment of the pre-molten material in the hearth furnace portion it is continuously supplied with pre-molten material which is subject to serious fluctuations in regard to its composition and temperature so that the treatment procedure in the hearth furnace is adversely affected thereby. Finishing of the molten material (deoxidation, further desulphurisation and alloying) is therefore to be effected outside the hearth furnace portion, for example during tapping into a ladle.
DE-25 04 911-A1 discloses an apparatus for smelting scrap, sponge iron or the like in a blast furnace by means of a fuel-oxygen flame from below and with an outlet for the molten material in the bottom of the blast furnace for the continuous production of steel, in which a heating vessel which is mounted laterally in relation to the blast furnace is integrated therewith. At the lowest point of its bottom the blast furnace has an outlet for molten metal which is connected to the superheating vessel by way of a passage and also a slag discharge in the side wall. The superheating vessel is provided with an overflow means which is disposed slightly beneath the level of the slag outlet. The liquid metal which is superheated in the superheating vessel flows away continuously by way of the overflow means and is continuously replaced by the liquid metal which is melted in the blast furnace, by way of a connecting passage to the blast furnace. The superheating vessel is heated by means of arcs.
The object of the present invention, in a metallurgical unit of the kind described in the opening part of this specification, is to prevent congealing of the molten material in the transfer region between the melting and the treatment vessels without additional heat energy having to be supplied to that region. The invention further seeks to provide that an adverse effect on the treatment procedure on the molten material in the treatment vessel, which is caused by a continuous feed flow of pre-molten metal which fluctuates severely in terms of its composition can be prevented. The invention further seeks to provide that the melting vessel and the treatment vessel can be of an optimum configuration and mode of operation, independently of each other, in terms of their aim. Finally the invention seeks to provide that the energy consumption of the unit per tonne of metal produced is minimised and the hot waste gases from the treatment vessel as well as the melting vessel can be put to use for preheating the charge material.